As is known, peaks and valleys in a winding are caused by irregularities in the surface of the spool core, the progressive overlapping of the wire layers, the loosening of winding tension due to problems with the path of the wire, etc.
The formation of peaks and valleys is also possible at a spool flange owing to the incorrect position of the flange; this is the case when, for example, the “effective winding width” of a spool is different from the pre-set one, taking into account the kind of spool.
The formation of peaks and valleys is also promoted by possible irregularities in the flange geometry (for example, the presence of deformed flanges); or fittings between the core, spool and flanges that are large in relation to the wire diameter or the size of the surrounding circle. Moreover, flanges can also be deformed during the progressive filling of the spool due to the pulling of the skein of wire.
Other causes of peak and valley formation can be, for example, loosening and/or delayed movement of the wire due to the reversal of the direction of movement of the wire dispensing device, or irregularities in the wire distribution due to size; for example, a wire with a large diameter tends to have an inertia that is difficult to control.
It is known, moreover, that in the winding operation there is a constant datum, regardless of the section, namely, the wire always tends to lag behind with respect to the movement of the wire dispensing device that distributes it. This phenomenon becomes more pronounced the further the wire dispensing device moves away from the spool and the more the cross-section of the wire increases.
In standard applications, both when the wire dispensing device is connected mechanically to the spool rotation and when the wire dispensing device is controlled separately, the linear translational speed of the wire dispensing device is kept constant throughout a single layer of deposited wire. This means that in the end there are no changes to the winding pitch in the various layers. In addition, during the gradual filling of the spool, the linear speed of the wire dispensing device decreases in such a way as to have a constant winding pitch as the diameter of the skein of wire wound on the spool increases.
For instance, in U.S. Pat. No. 7,370,823 B2 (NIEHOFF) a system is described that takes into account:                the wire speed;        the value of the winding diameter, calculated or detected by one or more sensors mounted on the wire dispensing device; and        the spool position and angular speed (through a speed or position detector), which are correlated in order to avoid the formation of peaks and valleys.        
At the flanges, the use of one or more sensors enables their position to be detected and, again taking the wire speed, the winding diameter and the spool angular position into account, these are correlated to define the presence of peaks and/or valleys and take immediate action to reverse the direction of the wire dispensing device in order to fill a valley (delaying the moment in which the direction is reversed or stopping the movement of the device) or not lay wire (by reversing the movement in advance).
Although the system described in U.S. Pat. No. 7,370,823 B2 (NIEHOFF) allows a fairly precise control of the wire winding on the spool, it is expensive and sometimes unreliable due to the fact that controls are performed by means of speed sensors.